© 2002 by CRC Press LLC is not as crucial, spray-up is the more suitable option. Bathtubs, swimming pools, boat hulls, storage tanks, duct and air handling equipment, and fur- niture components such as seatings are some of the commercial uses of this process. 6.8.3.2 Basic Raw Materials The reinforcement material for this process is glass fiber rovings, which are chopped to a length of 10 to 40 mm and then applied on the mold. For improved mechanical properties, a combination of fabric layers and chopped fiber layers is used. The most common material type is E-glass, but carbon and Kevlar rovings can also be used. Continuous strand mat, fabric, and various types of core materials are embedded by hand whenever required. The weight fraction of reinforcement in this process is typically 20 to 40% of the total weight of the part. The most common resin system used for the spray-up process is general- purpose or DCDP polyester. Isophthalic polyester and vinylesters are also used in this process. Fast-reacting resins with a pot life of 30 to 40 min are typically used. The resin often contains a significant amount of filler. The most common fillers are calcium carbonate and aluminum trihydrate mate- rials. In filled resin systems, fillers replace some of the reinforcements; 5 to 25% filler is used by weight. 6.8.3.3 Tooling Requirements The mold used in this process is identical to that used in the wet lay-up process. Male and female molds are used, depending on the application. Tubs and showers utilize male molds, whereas boat hulls and decks utilize female molds. To make bathtubs, FRP molds are used. The method used to make the mold is described in Section 6.4.3. 6.8.3.4 Making of the Part The processing steps used in the spray-up process are very similar to those in the wet lay-up process. In this process, the release agent is first applied to the mold and then a layer of gel coat is applied. The gel coat is left for 2 hr, until it hardens. Once the gel coat hardens, a spraygun is used to deposit the fiber resin mixture onto the surface of the mold. The spraygun chops the incoming continuous rovings (one or more rovings) to a predetermined length and impels it through the resin/catalyst mixture as shown in Figure 6.27. Figure 6.28 shows the application of chopped fibers and resin by a robot. Resin/catalyst mixing can take place inside the gun (gun mixing) or just in front of the gun. Gun mixing provides thorough mixing of resin and catalyst inside the gun and is preferred to minimize the health hazard concerns of the operator. In the other type, the catalyst is sprayed through two side nozzles into the resin envelope. Airless sprayguns are becoming © 2002 by CRC Press LLC is not as crucial, spray-up is the more suitable option. Bathtubs, swimming pools, boat hulls, storage tanks, duct and air handling equipment, and fur- niture components such as seatings are some of the commercial uses of this process. 6.8.3.2 Basic Raw Materials The reinforcement material for this process is glass fiber rovings, which are chopped to a length of 10 to 40 mm and then applied on the mold. For improved mechanical properties, a combination of fabric layers and chopped fiber layers is used. The most common material type is E-glass, but carbon and Kevlar rovings can also be used. Continuous strand mat, fabric, and various types of core materials are embedded by hand whenever required. The weight fraction of reinforcement in this process is typically 20 to 40% of the total weight of the part. The most common resin system used for the spray-up process is general- purpose or DCDP polyester. Isophthalic polyester and vinylesters are also used in this process. Fast-reacting resins with a pot life of 30 to 40 min are typically used. The resin often contains a significant amount of filler. The most common fillers are calcium carbonate and aluminum trihydrate mate- rials. In filled resin systems, fillers replace some of the reinforcements; 5 to 25% filler is used by weight. 6.8.3.3 Tooling Requirements The mold used in this process is identical to that used in the wet lay-up process. Male and female molds are used, depending on the application. Tubs and showers utilize male molds, whereas boat hulls and decks utilize female molds. To make bathtubs, FRP molds are used. The method used to make the mold is described in Section 6.4.3. 6.8.3.4 Making of the Part The processing steps used in the spray-up process are very similar to those in the wet lay-up process. In this process, the release agent is first applied to the mold and then a layer of gel coat is applied. The gel coat is left for 2 hr, until it hardens. Once the gel coat hardens, a spraygun is used to deposit the fiber resin mixture onto the surface of the mold. The spraygun chops the incoming continuous rovings (one or more rovings) to a predetermined length and impels it through the resin/catalyst mixture as shown in Figure 6.27. Figure 6.28 shows the application of chopped fibers and resin by a robot. Resin/catalyst mixing can take place inside the gun (gun mixing) or just in front of the gun. Gun mixing provides thorough mixing of resin and catalyst inside the gun and is preferred to minimize the health hazard concerns of the operator. In the other type, the catalyst is sprayed through two side nozzles into the resin envelope. Airless sprayguns are becoming . Making of the Part The processing steps used in the spray-up process are very similar to those in the wet lay-up process. In this process, the release agent is first applied to the mold and then. Making of the Part The processing steps used in the spray-up process are very similar to those in the wet lay-up process. In this process, the release agent is first applied to the mold and then. in this process is identical to that used in the wet lay-up process. Male and female molds are used, depending on the application. Tubs and showers utilize male molds, whereas boat hulls and decks